Recently, renewed interest has been given to energy consumption in information and communication technologies (ICT). Based upon exponential traffic growth trends, inadequate business-as-usual network equipment efficiency measures are expected to lead to unsustainable power requirements in the coming decades. Today energy costs for large service providers are substantial and in the case of mobile networks, can be a large component of operational expenses. In wireline networks, the deficit between equipment efficiency improvement and capacity growth has strained thermal management capabilities in central offices and brought focus to power in the design of telecommunications equipment.
According to some estimates, the carbon footprint today for all ICT is estimated to be only 1-2% worldwide and the network equipment contribution is roughly one-third with the remaining composed of data centers, personal computers, printers and peripherals. Further, these studies have pointed to power spent for ICT as an enabler for five-fold carbon footprint reductions in other sectors of society such as transportation or in-building controls. So-called smart technologies take advantage of ubiquitous monitoring and data collection provided by ICT to better control the energy consumed by a wide range of power systems from the power grid itself to household electronics. This benefit however, is dependent on the assumption that the total power associated with ICT will only see a modest increase (doubling in 10 years) without impact on the continued growth and availability of ICT resources such as bandwidth. These estimates do not take into account details associated with the relative growth of traffic and network equipment efficiency and the report admits to a high level of uncertainty on this issue.
Several technology trends raise concerns over the ability of technology efficiency improvements to keep pace with traffic growth. Most of the power in network equipment is dissipated in the electronics and thus efficiency improvements are strongly tied to Moore's law trends. In recent years, operating voltages and consequently the CMOS switching power has not kept pace with feature size reductions. Furthermore, chip energy consumption is increasingly becoming interconnect limited rather than CMOS switching energy limited. At the same time, the transport media itself, whether wireline or wireless, is being constrained by the minimum received energy given by the Shannon channel capacity. Mobile links typically operate within 3 dB of their respective Shannon limits. Laboratory optical transmission system experiments have reached within 4 dB of the Shannon limit. As a result, network capacity gains due to increasing spectral efficiency will diminish. In the past, the dramatic growth of wireline network capacity has largely been due to efficient bandwidth scaling of the interfaces, including the use of wavelength division multiplexing (WDM). Continued network growth without this scaling would result in an exponential growth in the number of interfaces and/or spectral width and associated network power consumption.
Studies of network energy use have shown that the power is dominated by the access equipment today, although the core network equipment will draw even with increasing traffic. Additional service-dependent traffic growth trends are needed to better understand how this evolution might be engendered in a particular network.
Therefore it would be desirable to have a transaction based power consumption model that includes enterprise switching and, for the core equipment, that includes equipment energy efficiency, in order that network alterations may be assessed for their impacts on power consumption.